Cuddling up with the Fragile X model mouse: new clues to sensory sensitivities in ASD

Fragile X is one of the genetic causes of autism spectrum disorders (ASD), responsible for about 5% of all the cases. This week Autism Speaks-funded researchers have taken a significant step toward understanding the brain mechanisms that may underlie the sensory sensitivities commonly observed in individuals with Fragile X syndrome.

Researchers from Northwestern University and the University of Edinburgh studied mice with deficits in the same protein that is missing in individuals with Fragile X (the protein is called FMRP). They examined brain cell connections in a brain area that responds to touch—whisker touch in the mouse. The research team found that development of these brain cell connections were significantly delayed n the FMRP-deficient mouse.

This delay in the development of cell connections happens during a critical period when the sensation of touch is developing. During this period, early sensory experiences help to establish the proper connections within cortex. These connections are less flexible later in development.

Sensory areas of the brain do not develop in isolation. A early delay in the development of brain connections involved in sensory processing, such as was observed in FMRP-deficient mice, can lead to disordered connections throughout the brain. Sensory hypersensitivities, social withdrawal and anxiety—all common symptoms of Fragile X syndrome, could result from disordered communication within the brain. This link has led some to speculate that “tactile defensiveness”, or discomfort experience when being touched or hugged, could be linked to these early sensory development differences during the critical period.

Importantly this research has highlighted the development of sensory cortices as a time window worthy of examination in other forms of ASD and also a target for potential treatments.